dga {labdsv}R Documentation

Direct Gradient Analysis

Description

Direct gradient analysis is a graphical representation of the abundance distribution of (typically) species along opposing environmental gradients

Usage

dga(z,x,y,step=25,pres="+",abs="-",labcex=1,
    xlab = deparse(substitute(x)), ylab = deparse(substitute(y)),
    pch = 1, title = "", ...)

Arguments

z the variable (typically a species abundance) to be plotted
x the variable to use as the x axis
y the variable to use as the y axis
step controls the grid density fed to the GAM surface fitter
pres the symbol to print when a species is present (presence/absence mode)
abs the symbol to print when a species is absent (presence/absence mode)
labcex the character size for contour labels
xlab the x axis legend
ylab the y axis legend
pch the symbol to print in continuous abundance plots
title the title to print
... miscellaneous arguments to pass to par

Details

‘dga’ interpolates a grid of x,y values from the supplied data and fits a GAM (from mgcv) of the z variable to the grid. The GAM surface is then represented by a contour map and abundance symbols as described above.

Value

a graph of the distribution of the z variable on a grid of x and y is displayed

Note

Direct gradient analysis was promoted by Robert Whittaker and followers as a preferred method of vegetation analysis.

Author(s)

David W. Roberts droberts@montana.edu http://ecology.msu.montana.edu/labdsv

References

http://ecology.montana.msu.edu/labdsv

See Also

gam

Examples

    data(bryceveg) # returns a data.frame called bryceveg
    data(brycesite)
    dga(bryceveg$arcpat,brycesite$elev,brycesite$grorad)

[Package labdsv version 1.0-1 Index]